support azure loadbalancer standard sku (#4150) (#4476)

add the support of the folling property in azure-credential-check.yml
  - azure_loadbalancer_sku: Sku of Load Balancer and Public IP. Candidate values are: basic and standard.
  - azure_exclude_master_from_standard_lb: excludes master nodes from standard load balancer.
  - azure_disable_outbound_snat: disables the outbound SNAT for public load balancer rules
  - useInstanceMetadata: Use instance metadata service where possible
  - azure_primary_availability_set: (Optional) The name of the availability set that should be used as the load balancer backend